Electro mechanical brake tightening device

ABSTRACT

An electromechanical brake tightening device for a rail vehicle, includes a brake actuator to apply and release brakes. The actuator has a power converter to convert energy supplied by the brake actuator to a brake application movement. The power converter includes a shear force measuring bolt and/or a brake lever, arranged in a power transmission path of the converter to measure braking power.

BACKGROUND

The present disclosure relates to an electromechanical brake tighteningdevice, particularly for a rail vehicle brake.

Currently, three braking systems are essentially used in the railvehicle sector: Electropneumatic braking systems, electrohydraulicbraking systems as well as electromechanical braking systems. Thebraking system may be constructed as an active or passive brakingsystem, depending on whether the force of a brake actuator has to beapplied for braking (active braking system) or for releasing the brake(passive braking system). In the event of operating disturbances, anenergy accumulation takes place in compressed-air reservoirs in the caseof electropneumatic systems, in hydraulic reservoirs in the case ofelectrohydraulic systems and, in the form of pre-loaded springs in thecase of electromechanical systems.

From the prior art, electromechanical brake tightening devices for railvehicles are known which have a brake actuator which comprises a servicebrake unit as well as an accumulator-type brake unit having an energyaccumulator. The service brake unit contains a braking power generatorfor the application and/or release of the brake, for example, in theform of an electric motor drive. The accumulator-type brake unitcomprises at least one energy accumulator for storing and supplyingenergy for the application of the brake as a service-type emergencybrake in the sense of an underlying safety plane in the event of afailure of the service brake unit and/or as the parking brake. Theaccumulator-type brake unit is generally constructed as a spring-loadedbrake.

A power converter provides a conversion of the energy supplied by thebraking power generator and/or by the energy accumulator into a brakeapplication movement. The electric-motor drive can be controlled by anelectronic control and power system to carry out slip-controlled orload-corrected brakings. For the desired-actual comparison, values arerequired for the respectively present actual braking power, so thatsensors for the direct braking power measurement or for measuringquantities from which the actual braking power can be derived have to beprovided.

In the case of electropneumatic and electrohydraulic braking systems,pressure sensors are generally used for measuring the operating pressureexisting in the compressed air or in the hydraulic liquid, from whichoperating pressure the amount of the momentary braking power can then bederived. However, such mediums do not exist in the case ofelectromechanical systems.

SUMMARY

The present disclosure relates to an electromechanical brake tighteningdevice for a rail vehicle which permits a measuring of braking power ina simple and precise manner.

The electromechanical brake tightening device includes a brake actuatorto apply and release brakes. The actuator has a power converter toconverter energy supplied by the brake actuator to a brake applicationmovement.The power converter includes a shear force measuring boltand/or a brake lever, arranged in a power transmission path of theconverter to measure a braking power.

The mechanical-to-electrical shear force measuring bolt combines twofunctions by converting power and simultaneously measuring power. Forthis reason, the brake tightening device according to the presentdisclosure, on the one hand, can have a small construction and, on theother hand, the number of component parts and the weight are reduced.The fact that the power or force sensor is directly integrated in thepower flux or power transmission path of the power converter, inaddition,results in a high measuring accuracy. For ensuring a reliablepower transmission, the shear force measuring bolt can mechanically bedesigned to have a high fatigue strength.

According to an embodiment of the device, the shear force measuring boltforms a hinge bolt of a hinge mutually connecting at least two powertransmission elements of the power converter. The hinge couples aconnecting rod, which can be linearly operated by the brake actuator, toa brake lever of an eccentric arrangement acting upon brake shoes. As aresult, the power measuring point is in the direct vicinity of the pointof the power effect, which is why the influence of disturbancevariables, such as the bearing friction or hysteresis, is low,permitting very precise measurements.

An embodiment provides that the sensor measuring the braking powercontains at least one strain gauge held on the circumference of theshear force measuring bolt. It is known that strain gauges have a highmeasuring precision with a simultaneously broad measuring range and areinsensitive to temperature changes and pressure surges, which isapplicable mainly in the case of the force effect occurring abruptlyduring emergency braking. Furthermore, they are distinguished by a goodlong-term stability as well as a high corrosion resistance.

According to another embodiment, redundant measuring sensors and/orredundant electronic sensor signal analyzing systems, particularlyredundant measuring sensors with different measuring principles and/orredundant electronic sensor signal analyzing systems of differentconstructions and types are provided. Such a configuration may result inan increased reliability of the measuring arrangement. In addition, aplausibility check can be carried out by comparing the measuring signalsof two or more measuring circuits.

Other aspects of the present disclosure will become apparent from thefollowing descriptions when considered in conjunction with theaccompanying drawings.

DRAWINGS

FIG. 1 is a sectional view of an embodiment of a brake actuator havingan integrated shear force measuring bolt, according to the principles ofthe present disclosure.

FIG. 2 is a sectional view of the shear force measuring bolt of FIG. 1along Line II—II.

DETAILED DESCRIPTION OF THE DRAWINGS

An embodiment of an electromechanical brake tightening device 1, for arail vehicle as shown in FIG. 1, includes a brake actuator 2 having aservice brake unit and an accumulator-type brake unit. The service brakeunit has an electric drive, for example, an electric servo motor 4,which is accommodated in an actuator housing 6 of the brake actuator 2.A mechanical power converter 8 is used for converting the energysupplied by the brake actuator 2 to a brake application movement.

The servo motor 4 causes a coaxial brake spindle 10 to carry outrotations which are converted by the power converter 8 to a brakeapplication movement of brake pads 12 in the direction of a brake disk14. The power converter 8 comprises, among other parts, a constructionalspindle/nut unit 16 with a spindle nut 18 rotatably disposed on thebrake spindle 10, which spindle nut 18 can carry out linear movements ina direction of the spindle axis when the brake spindle 10 is rotated.The end of the brake spindle 10 facing away from the servo motor 4projects into a cylindrical hollow section of a connecting rod 20 whichis connected in an axially fixed manner with the spindle nut 18. Inaddition, the cylindrical hollow section of the connecting rod 20 isheld in an axially fixed manner in a sliding sleeve 22 against which atleast one pre-loaded spring 24, which is supported on the actuatorhousing 6, is prestressed in a brake release position. The pre-loadedspring 24 is part of the accumulator-type brake unit. It is used as anenergy accumulator for storing and supplying energy for applying thebrake as a service-type emergency brake in the sense of a safety backupin the event of a failure of the service brake unit and/or as a parkingbrake. The service brake unit as well as the accumulator-type brake unitact upon the connecting rod 20. The pre-loaded spring 24 is held in theprestressed position by means of a locking device 26.

A plate-shaped connecting rod head 28 of the connecting rod 20 projectsout of the sliding sleeve 22 and is provided with a connecting rod eye30. As illustrated particularly in FIG. 2, a hinge bolt 32 extendsthrough the connecting rod eye 30 as well as passage bores 34 coaxialthereto of cheeks 38 axially on both sides of the connecting rod eye 30and head 28. The cheeks 38 are constructed at an end of a brake lever36. The cheeks 38 of the brake lever 36, the connecting rod head 28 andthe hinge bolt 32 together form a hinge 40 of the power converter 8,whereby the brake lever 36 is linked perpendicularly to the spindle axis42 to the connecting rod 20. The brake lever 36 and connecting rod 20are at least two power transmission elements of the power converter 8.When the brake spindle 10 is driven in a brake application direction orwhen the locking device 26 of the pre-loaded spring 24 is released, as aresult of the then axially moving-out connecting rod 20, the hinge bolt32 is stressed, among other things, by shear forces applied essentiallyperpendicular to the bolt axis 44.

The other end of the brake lever 36 acts upon an eccentric arrangementhaving an eccentric shaft 46 which is linked to a caliper lever 48which, together with another caliper lever 50, forms a caliper 52. Atone end of the calipers 48, 50, pad holders 54 are arranged which havebrake pads 12 displaceable in a direction of an axis of the brake disk14. Ends of the caliper levers 48, 50 facing away from the brake pads 12are connected with one another by way of a plunger rod adjuster 56 whichis preferably designed to be electrically operated. The describedarrangement also forms a part of the power converter 8 which convertsthe moving-out motion of the connecting rod 20 caused by the servo motor4 or by the pre-loaded spring to a brake application movement of thebrake pads 12 in the direction of the brake disk 14.

According to the present disclosure, the hinge bolt 32 of the hinge 40is formed by a shear force measuring bolt 58. The shear force measuringbolt is equipped with at least one measuring sensor 60 that measuresquantities from which the braking power acting at the brake pads 12 canbe derived in an indirect or direct manner. In an embodiment, themeasuring sensor 60 may be formed by strain gauges (DMS) which areaccommodated, for example, in recesses or grooves 62 extending around ina plane perpendicular to the bolt axis 44. The grooves 62 with thestrain gauges 60 are situated in an area of axial junction points orplanes of the connecting rod head 28 with the cheeks 38 of the brakelever 36 and therefore precisely in shearing planes of the shear forcemeasuring bolt 58 stressed by shear. The strain gauges 60 are fastenedto the circumference of the shear force measuring bolt 58 preferably bygluing in such a manner that they generate signals proportional to theshearing deformations of the shear force measuring bolt 58 caused by theshear forces acting in opposite directions, and supply these signals toan electronic analyzing system 64.

As an alternative, the grooves 62 may be eliminated and the straingauges 60 may be fastened directly to an exterior surface of the shearforce measuring bolt 58. According to another alternative or inaddition, strain gauges 60 may be held in a hollow bore of the shearforce measuring bolt 58 coaxial to the bolt axis 44. The shear forcemeasuring bolt 58 may thus have a thin-walled construction. Instead ofbeing fastened to the shear force measuring bolt 58, or in additionthereto, one or more strain gauges 60 may also be arranged on the brakelever 36, in order to be able to derive braking power from deformationsof the brake lever 36.

Furthermore, any other type of measuring sensor can be used by whichdeformations of the shear force measuring bolt 58 and/or of the brakelever 36 occurring during operation can be measured. Thus, for example,pressure-measuring transducers may be integrated in the shear forcemeasuring bolt 58 and may operate according to a capacitive, apiezoelectric or a piezoresistive principle. In order to achieve areliability of the measuring arrangement which is as high as possible,the measuring sensors 60 and/or the electronic analyzing system 64 maybe provided in a redundant manner. In particular, redundant measuringsensors 60 with different measuring principles and redundant electronicanalyzing systems 64 of a different construction and type may also bepresent.

The shear force measuring bolt 58 has an end-side bolt head 66 which hasan enlarged diameter and in which an electronic sensor signal analyzingsystem 64 is accommodated. The system 64 may be cast into the bolt head66, whereby a vibration-damping or vibration-uncoupling accommodation isprovided. In the embodiment strain gauges 60, the electronic analyzingsystem 64 may include a straingauge bridge circuit (not shown). Inmounted condition, a face-side ring surface of the bolt head 66 impactsaxially on an upper cheek 38 of the brake lever 36. The end of the shearforce measuring bolt 58 pointing away from the bolt head 66 has twoexterior grooves 68, which extend transversely with respect to the boltaxis 44, to receive a position-securing snap ring (not shown).

A conversion of shear deformation signals to signals for respectiveactual values for the momentary braking power acting at the brake pads12 also takes place in the electronic analyzing system 64. Those signalsare transmitted to a control and regulating device, which is not shown,in order to be able to set a desired braking power by a desired-actualcomparison. Furthermore, the received signals for the actual values forthe momentary braking power are used for monitoring the power input andthe operability of the brake tightening device 1 during safety-relevantbrakings. In addition, for verifying the measuring results, a motorcurrent measured on a drive-side by a current sensor can be balancedwith the signal for the actual values for the momentary braking power.

Although the present disclosure has been described and illustrated indetail, it is to be clearly understood that this is done by way ofillustration and example only and is not to be taken by way oflimitation. The spirit and scope of the present disclosure are to belimited only by the terms of the appended claims.

1 Brake tightening device 2 brake actuator 4 servo motor 6 actuatorhousing 8 power converter 10 brake spindle 12 brake pad 14 brake disk 16spindle-nut constructional unit 18 spindle nut 20 connecting rod 22sliding sleeve 24 pre-loaded spring 26 locking device 28 connecting rodhead 30 connecting rod eye 32 hinge bolt 34 passage bores 36 brake lever38 cheeks 40 hinge 42 spindle axis 44 bolt axis 46 eccentric shaft 48caliper lever 50 caliper lever 52 caliper 54 pad holder 56 plunger rodadjuster 58 shear force measuring bolt 60 measuring sensor (straingauge) 62 grooves 64 electronic analyzing system 66 bolt head 68exterior grooves.

1. An electromechanical brake tightening device for a rail vehicle, comprising: a brake actuator to apply and release brakes, having a power converter to convert energy supplied by the brake actuator to a brake application movement; the power converter including at least one of a shear force measuring bolt and a brake lever, arranged in a power transmission path of the converter to measure a braking force: the shear force measuring bolt being equipped with at least one measuring sensor measuring braking power at least one of indirectly and directly: and wherein the shear force measuring bolt has an end-side bolt head which has an enlarged diameter and in which an electronic sensor signal analyzing system is arranged.
 2. The electromechanical brake tightening device according to claim 1, wherein the shear force measuring bolt forms a hinge bolt of a hinge, mutually connecting at least two power transmission elements of the power converter.
 3. The electromechanical brake tightening device according to claim 2, wherein the power transmission elements are a connecting rod and a brake lever, and the hinge connects the connecting rod, which is linearly operable by the brake actuator, with the brake lever that acts on an eccentric arrangement acting upon brake pads.
 4. The electromechanical brake tightening device according to claim 3, wherein the shear force measuring bolt projects through a connecting rod head of the connecting rod and through passage bores coaxial thereto of cheeks of the brake lever axially on both sides of the connecting rod head.
 5. The electromechanical brake tightening device according to claim 1, wherein the brake lever acts upon an eccentric arrangement having an eccentric shaft which is linked to at least one caliper lever which, together with another caliper lever, forms a caliper, and pad holders with brake pads are arranged at ends of each of the caliper levers, which brake pads are displaceable in a direction of an axis of a brake disk.
 6. The electromechanical brake tightening device according to claim 1, wherein the at least one measuring sensor includes least one strain gauge held on at least one of a circumference of the shear force measuring bolt and a circumference of the brake lever.
 7. The electromechanical brake tightening device according to claim 1, wherein the at least one measuring sensor includes at least one strain gauge held in a hollow bore of a thin-walled shear force measuring bolt.
 8. The electromechanical brake tightening device according to claim 6, wherein recesses accommodating the at least one strain gauge are provided on the circumference of the shear force measuring bolt, which recesses are situated in an area of axial junction planes of a connecting rod head with cheeks of the brake lever.
 9. The electromechanical brake tightening device according to claim 1, further including at least one measuring sensor measuring braking power and including at least one pressure-measuring transducer integrated in the shear force measuring bolt and operating according to one of a capacitive, piezoelectric and piezoresistive principle.
 10. The electromechanical brake tightening device according to claim 1, wherein the electronic sensor signal analyzing system is cast into the bolt head such that at least one of vibration-damping and vibration-uncoupling is provided.
 11. The electromechanical brake tightening device according to claim 1, wherein at least one of redundant measuring sensors and redundant electronic sensor signal analyzing systems, are provided.
 12. The electromechanical brake tightening device according to claim 1, further including a measuring sensor, by which actual values of momentary braking power are supplied as signals to a regulating device.
 13. The electromechanical brake tightening device according to claim 1, wherein the brake actuator includes an electric motor whose motor current can be detected by a current sensor.
 14. The electromechanical brake tightening device according to claim 13, wherein a signal for the motor current can be balanced with a signal for the braking power.
 15. The electromechanical brake tightening device according to claim 1, wherein the at least one measuring sensor measures the braking power directly.
 16. The electromechanical brake tightening device according to claim 1, wherein the at least one measuring sensor measures the braking power indirectly.
 17. The electromechanical brake application device according to claim 11, wherein the redundant sensors include different measuring principles.
 18. The electromechanical brake tightening device according to claim 11, wherein the redundant electronic sensor signal analyzing systems are of different construction. 